How do architecture, IT and information security work together around ISO 27001, and what does each contribute?

Architecture designs the plan and demands a secure construction; the IT department builds and operates the cyber system following the plan; information/IT security sets requirements, using ISO 27001 as its template, and demands that the system is securely manageable. The goal is that these requirements meet without conflict.

The system has to satisfy both requirements at once. A design that is secure on paper but cannot be operated according to the ISMS processes fails, and so does a well-managed system built on an insecure construction. The architect's job includes making the two meet without conflict.